Prior to the early 1970's pipe line construction across bodies of water consisted of laying the pipeline under water and anchoring it to the bed or floor of the body of water. Over a period of time, the pipe would shift and rise and it would be necessary for underwater divers to reanchor the pipe. In large bodies of water, pipelines can shift up to a mile from their original position. In the early 1970s, a drilling rig was developed capable of drilling a tunnel horizontally under the body of water and a cable could be pulled through the tunnel to maintain the cable or pipe securely in position. Similarly, larger tunnels were dug, for example for sewer pipes, and the pipe hydraulically forced into the tunnel.
Generally, this procedure is called horizontal directional drilling or pipe jacking. The drilling rig directionally tunnels, generally horizontally, while conveying the extracted soil out of the tunnel being excavated. In small diameter cable or pipeline operations, a soil stabilizing composition, such as a bentonite slurry, is pumped outwardly from the face of the drill bit or from a reaming device to stabilize the soil and generally fill the tunnel with the stabilizing composition. Thereafter, the small diameter cable or pipe is pulled from one end of the tunnel to the opposite end while the bentonite slurry serves as a soil stabilizing and lubricating composition to stabilize the tunnel walls and lessen the frictional forces between an outer surface of the cable or pipe and the tunnel walls.
In larger diameter pipe laying operations, such as a sewer pipe, a stabilizing and lubricating composition, such as a bentonite slurry, is pumped through an aperture in the pipe by a manually installed hose connected from the interior of the pipe to a nozzle extending outwardly from an outer surface of the pipe. The composition lubricates the outer surface of the pipe and lessens the friction between the pipe outer surface and the tunnel walls while the pipe is forced or hydraulically jacked in sections into the tunnel. The bentonite slurry, in either case, fills the space between the outer surface of the cable or pipe and the tunnel walls to stabilize the tunnel walls during the positioning of the cable or pipe within the tunnel, and, by substantial friction lessening, dramatically increases the efficiency of the installation.
Pipe jacking has become an economical and effective alternative to other traditional open-cut methods and to monolithic mining methods previously used for installation of sewer pipes. In the pipe jacking operation, the predominant concern is to minimize friction between an outer surface of the pipe and the tunnel walls. The frictional forces between the outer surface of the pipe and the tunnel determines the distance and the amount of pipe that can be pushed from a single shaft. Each time a new shaft must be dug, productivity decreases and cost increases. This and the need to drive longer lengths of pipe greater and greater distances has increased the need for consistently high performing friction reducing agents.
The friction between the tunnel and the pipe increases in accordance with the distance between the jack and the leading pipe edge and the type of soil that the pipe is being pushed into. The frictional resistance between the tunnel wall and the pipe surface is relatively small when pipe jacking through a soil having a high clay content and relatively large through soils having a high sand or shale content.
The composition of the present invention combines with the soil to form a stable surface on the tunnel walls and the remaining composition acts as a slip agent between the tough, flexible soil surface and the outside pipe surface to unexpectedly lower the amount of hydraulic pressure needed to push the pipe into the tunnel. This reduced friction enables the hydraulic jack to push more pipe a greater distance along a tunnel, thereby lowering the cost of installation and increasing the speed and accuracy of operation.
In accordance with the present invention, quite unexpectedly it has been found that by including magnesium oxide in a water swellable clay composition in an amount of only 0.025-0.5% based on the dry weight of the clay, and using this composition as a lubricating composition disposed between the outer surface of the cable or pipe and the tunnel walls, the frictional forces between the cable or pipe and the tunnel walls are unexpectedly lessened to unexpectedly improve the efficiency of cable or pipe installation.
Others have included magnesium oxide in a bentonite clay composition for the purpose of increasing the viscosity of the bentonite slurry for better carrying of drill cuttings out of a drill hole and for fluid-tight sealing in agglomeration of foundry sands as disclosed inthe Bailey Pat. No. 4,014,394; the Chavrier Pat. No. 3,115,416 and the Forster et al Pat. No. 4,209,409. Further, the Callahan Jr. Pat. No. 3,309,313 discloses the use of magnesium oxide for use in an oil-based lubricating composition for stainless steel or other metal alloys subjected to temperatures ranging from 500.degree. F. to 2400.degree. F. As disclosed in the Callahan Jr. patent, the primary purpose of the magnesium oxide is to make the metal oxides, which are usually formed on the threaded surfaces at these temperatures, easier to rupture. As disclosed in the above-cited patents, when magnesium oxide is included in a well drilling composition to increase viscosity and improve lifting of drill cuttings, the magnesium oxide is included in a minimum amount of about 0.75% based on the dry weight of the clay in the composition.